Instructables
IMPORTANT I have recently dug this out of a box and tried to regulate 9v from an RC car battery, it did work, but then there was a puff of smoke and it became extremely hot. This may be because i have previously fried the regulator, but i thought i would let you all know so you can be careful. I may need some filtering capacitors, not sure. please tell me if you have any ideas.

This is the circuit for converting a 12V car supply to 4.5V. 

You will need:
2 X 2 wire PCB mounted terminal blocks (optional) 
1 X diode
1 X L78S05CV voltage regulator chip 
Some verro board
Some Wire
 
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Step 2: Connect the wire jumps

Picture of Connect the wire jumps
 Solder the jump wires in.